The present invention relates to a catalytic component based on Vanadium supported on an inert solid matrix, which can be used in the production of ethylene propylene (EP) elastomers and ethylene propylene diene (EPDM) terpolymers in processes of the heterogeneous type as the suspension or the gas phase, preferably in suspension.
Elastomers which can be obtained using the catalytic component of the present invention are characterized by a better morphology and the polymerization process is characterized by a substantial absence or large reduction in the fouling of the reactor.
The first document which describes supported catalysts based on Vanadium, useful for the preparation of EP elastomers, is GB-A-1.309.303. Elastomeric polymers are produced in a liquid medium consisting of one of the monomers and in the presence of a supported catalyst of the Ziegler-Natta type comprising a halide of a metal belonging to groups IVB, VB, VIB and an organometallic compound.
GB-A-2.105.355 describes the use of supported catalysts based on Vanadium in the preparation of EP elastomers in gas phase. The support is selected from inorganic oxides and mixed oxides such as silica, alumina, Magnesium oxide, Titanium oxide and aluminium silicates; carbon black; zeolites; silicon carbide; minerals containing magnesium, aluminium and silicon, such as talc and kaolin. The above inert support is impregnated with an Aluminium alkyl, preferably chlorinated, and an oleosoluble compound of Vanadium (III) or (V). The molar ratio Al/V is between 10/1 and 200/1, preferably between 20/1 and 60/1.
U.S. Pat. No. 5,002,916 describes a catalytic component supported on an inert matrix, represented by the formula:
(A) (V3O(RCO2)6(ED)3)2.V2O2X6
or
(B) V3O(RCO2)6(ED)3
wherein
R is selected from alkyl, cycloalkyl, aryl and haloalkyl;
ED is an electron donor selected from alkyl and aromatic carboxylic acids, esters, ketones, amines and alcohols;
X is selected from chloride, bromide, fluoride and RCO2.
The solutions proposed in both the English and American documents however have some disadvantages.
In fact for the solution proposed by GB""355 both the Aluminium and the Vanadium necessary for the polymerization are totally deposited on the inert support. In other words, the supported catalyst described in the English patent is not a catalytic component, but a real catalyst which excludes the use of other cocatalysts. In addition the solution proposed in this document can only be used in polymerization in gas phase, not in a liquid one.
As far as the supported catalytic component described in U.S. Pat. No. 5,002,916 is concerned, this relates to a component which uses particularly valuable raw materials, requires a particularly difficult preparation process and in addition the elastomeric compositions which can be obtained have the inconvenience of having a certain degree of crystallinity.
A catalytic component for the preparation of EP elastomers has now been found which overcomes the above disadvantages.
In accordance with this the present invention relates to a process for the polymerization of ethylene with propylene and optionally another diene, said process being carried out in a suspension of a liquid monomer, in the presence of a catalyst containing Vanadium and a cocatalyst basically consisting of an organic compound of Aluminium and optionally in the presence of a halogenated promotor, characterized in that the catalyst containing Vanadium is supported on an inert matrix and is prepared by:
a) impregnation of an inert support with a solution, in hydrocarbons or halohydrocarbons, of a Vanadium compound with an oxidation state of between 3 and 5;
b) possible removal, from the impregnated support obtained in step (a), of the solvent used in step (a);
c) treatment of the inert material impregnated with Vanadium of step (a) or (b), with a hydrocarbon solution of a compound having general formula (I) RnAlXm wherein R is a C1-C20 alkyl radical, X is a halogen, n+m=3, and m is an integer from 0 to 2, the above step (c) being carried out in an inert atmosphere, preferably in an atmosphere of ethylene or alpha-olefins, the molar ratio between Aluminium of step (c) and Vanadium of step (a) being between 1/1 and 6/1, preferably between 1.5/1 and 3.0/1.
d) optional separation and purification of the catalyst containing Vanadium obtained in step (c).
The term inert matrix refers to inorganic oxides and mixed oxides such as silica, alumina, Magnesium oxide, Titanium oxide and aluminium silicates; carbon black; zeolites; silicon carbide; minerals containing magnesium, aluminium and silicon, such as talc and kaolin alumina, Magnesium oxide. The term inert matrix also refers to inert polymeric supports, such as stryrene-divinylbenzene copolymer.
The above inert supports preferably have an average diameter of between 5 and 400 xcexc, preferably between 10 and 120 xcexc; in fact it may be difficult to transport and suspend very large particles in the solvent whereas, on the other hand, it may be difficult to recover very fine particles.
The inert support has a sufficient quantity of sites on the surface to fix the catalyst by complexation or chemical bond. It is preferable for the inert support to have a high surface area and porosity which allow free access of the reagents to the catalytic sites. Surface areas of between 10 and 1000 m2/g and a porosity of between 0.1 and 4 ml/g are therefore preferable, and a porosity of between 1.0 and 2.5 ml/g is even more preferable.
In the preferred form of embodiment, the inert matrix is selected from alumina and silica, silica is even more preferable.
It is well known that inorganic oxides can contain water absorbed on the surface. As water is poisoning for the catalyst, it is necessary to subject the inert support to thermal treatment to reduce the content of water to very low levels, usually less than 2000 ppm, preferably less than 1000 ppm. In addition it is also preferable to eliminate traces of Oxygen from the pores of the support, for example by evacuating and pressurizing the above support various times with a dry inert gas, for example nitrogen or ethylene itself.
In step (a) the Vanadium compound is dissolved in a solvent selected from hydrocarbons and halohydrocarbons; typical examples of hydrocarbon solvents are toluene, benzene, heptane; typical examples of halohydrocarbons are dichloromethane, carbon tetrachloride, tri or tetrachloroethane. Other solvents or co-solvents, for example ethers, however can also be used, provided that the quantity does not jeopardize the solubility of the Vanadium compound.
In the preferred form of embodiment the solvent is dichloromethane.
The Vanadium compound used in step (a) is a Vanadium salt soluble in hydrocarbons in which the valence of Vanadium is between 3 and 5. Mixtures of these Vanadium compounds can obviously be used. Non-limiting examples of these compounds are:
Vanadyl trihalides, alkoxyhalides and alkoxides such as VOCl3, VOCl2(OBu) and VO(OC2H5)3;
Vanadium tetrahalides and Vanadium alkoxyhalides such as VCl4 and VCl3(OBu);
Vanadium and Vanadyl acetyl acetonates and chloro acetyl acetonates, such as V(AcAc)3, VOCl2(AcAc), VO(AcAc)2 wherein (AcAc) is an acetylacetonate;
Complexes between Vanadium halide and Lewis bases such as VCl3.2THF wherein THF is tetrahydrofuran.
In the preferred form of embodiment the Vanadium is V(III) acetyl acetonate.
The quantity of Vanadium reacted with the inert support is almost totally adsorbed on the matrix itself.
At the end of step (a) the inert support has a content of Vanadium of between 0.01 and 1 mmole of Vanadium per gram of support, preferably between 0.1 and 0.5 mmoles per gram of support.
The impregnation operation (step a), is carried out by putting the inert support in contact, preferably under stirring, with the solution of Vanadium compound. This operation is normally carried out at a temperature of between 10 and 40xc2x0 C. and for a time which depends on the concentration and quantity of Vanadium; a time of between 5 minutes and 2 hours is usually sufficient to ensure impregnation of the inert matrix, but higher times do not cause any inconvenience. Step (a) is carried out in an environment of inert gas, for example in an atmosphere of nitrogen, argon or helium.
The above step (a) is carried out by putting the inert support in contact with a solution of Vanadium, the volume of the above solution preferably being about the same as the total porosity of the inert support.
Operating in this way, at the end of step (a) a humid but flowing powder is obtained which can be dried or used as such. A much higher volume can be used however, which is then dried.
When step (a) has been carried out, the dispersion thus obtained can be used as such for step (c), or the solvent can be removed (step b) from the solid obtained in step (a). This can be carried out with the conventional techniques, for example by filtration and subsequent drying of the solid, or by simple drying of the impregnated solid obtained in step (a).
As in step (a), also step (c) is carried out in an inert atmosphere. However, in a preferred form of embodiment, step (c) is carried out in an atmosphere of ethylene, or a mixture of ethylene and alpha-olefin, the latter in liquid or gas form, so as to cover the support granule with a layer of homo or copolymer, thus obtaining a prepolymerized catalyst.
Among the compounds having general formula (I) RnAlXm wherein R is a C1-C20 alkyl radical, X is a halide, n+m=3, and m is an integer from 0 to 2, which can be used in step (c), alkyl Aluminium chlorides, such as Al(C2H5)2Cl, Al(C2H5)Cl2 are particularly useful, the most preferred being diethylaluminium chloride (DEAC).
The catalytic component obtained in step (c) can be used in the polymerization phase as it is obtained, or it can preferably be separated and purified with the normal separation and purification techniques, for example filtration and washing.
The catalytic component thus prepared at the end of step (c) is used in the preparation of EP copolymers together with a cocatalyst having general formula (I). The above cocatalyst can be the same as or different from the organic compound of Aluminium used in step (c). Dialkyl Aluminium chlorides, particularly diethylaluminium chloride, are particularly useful as cocatalyst. The molar ratio between cocatalyst and Vanadium can vary from 5 to 1000, preferably from 9 to 60.
In the copolymerization process, as well as the supported catalyst of the present invention and cocatalyst, it is preferable, as known to experts in the field, also to use a catalysis activator. These activators usually belong to the group of chlorinated organic compounds, for example ethyl trichloroacetate, n-butyl perchlorocrotonate, diethyl dichloromalonate, carbon tetrachloride, chloroform. The molar ratio between activator and Vanadium can vary from 0/1 to 1000/1, preferably from 0.5/1 to 40/1, even more preferably from 1/1 to 10/1.
The process of the present invention relates to the copolymerization of ethylene with higher alpha-olefins.
The process of the present invention is carried out in suspension, in a reaction medium (in a liquid or gas phase, but preferably in a liquid phase) in which the polymer is basically insoluble. In the preferred form of embodiment the reaction medium prevalently consists of one of the comonomers, to which a saturated hydrocarbon, such as propane, butane, pentane or hexane or aromatics, preferably propane, is optionally added as diluent.
The polymerization temperature is maintained at between xe2x88x925xc2x0 C. and 65xc2x0 C., preferably between 25 and 50xc2x0 C. The contact times vary from 10 minutes to 6 hours, preferably from 30 minutes to 1 hour.
The polymerization is generally carried out in the presence of hydrogen as moderator and regulator of the molecular weight, operating at a total pressure of between 5 and 10 bars, preferably between 8 and 30 bars, with a ratio between partial pressure of ethylene and partial pressure of hydrogen of more than 4, preferably higher than 20. Other components can however be used as molecular weight regulators, for example diethylzinc.
The elastomeric copolymers which can be obtained with the process of the present invention contain from 35% to 85% by weight of ethylene, preferably from 45% to 75% by weight and have a Mooney viscosity, ML1+4 at 125xc2x0 C., of between 5 and 120, preferably between 15 and 90.
The term higher alpha-olefins means alpha-olefins having a number of carbon atoms of between 3 and 10, for example propylene, butene-1, pentene-1. In particular the process of the present invention relates to elastomeric ethylene-propylene copolymers.
As is known to experts in the field, ethylene and higher alpha-olefins can be copolymerized with other monomers to give elastomeric terpolymers (EPDM). These termonomers can be selected, as known to experts in the field, from:
dienes with a linear chain such as 1,4-hexadiene and 1,6-octadiene;
acyclic dienes with a branched chain such as 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; 3,7-dimethyl-1,7-octadiene; dihydro myrcene and dihydrocymene;
alicyclic dienes with a single ring such as 1,4-cyclohexadiene; 1,5-cyclooctadiene; 1,5-cyclododecadiene;
dienes having condensed and bridged alicyclic rings such as methyltetrahydroindene; dicyclopentadiene; bicyclo-(2,2,1-)-hepta-2,5-diene; alkenyl, alkylidene, cycloalkenyl and cycloalkylidene norbornenes such as 5-methylene-2-norbornene (MNB); 5-ethylidene-2-norbornene (ENB); 5-propenyl-2-norbornene; 5-isopropenyl-2-norbornene; 5-(4-cyclopentenyl)2-norbornene; 5-cyclohexylidene-2-norbornene.
Among the non conjugated dienes typically used for preparing these copolymers, dienes containing at least one double bond in a tensioned ring are preferred. The third monomer which is mostly preferred is 5-ethylidene-2-norbornene (ENB).
Apart from the minimum fouling of the autoclave, the process of the present invention allows copolymers to be produced which, with the same composition, have a lower crystallinity than those of the prior art.